Shell: Use default constructors/destructors

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#cother-other-default-operation-rules

"The compiler is more likely to get the default semantics right and
you cannot implement these functions better than the compiler."

Userland/Shell/SyntaxHighlighter.cpp

@@ -581,8 +581,4 @@ bool SyntaxHighlighter::token_types_equal(u64 token0, u64 token1) const
     return token0 == token1;
 }
 
-SyntaxHighlighter::~SyntaxHighlighter()
-{
-}
-
 }